As a conventional torque limiter, a torque limiter is described in JP-A-62-159815 (Patent Document 1). In this torque limiter, an inner circumferential surface of a cylindrical member is fitted on an outer circumferential surface of a shaft member. Hydraulic oil is supplied into a hydraulic expansion chamber in the cylindrical member. The inner circumferential surface of the cylindrical member is contracted diametrically by the hydraulic oil in the hydraulic expansion chamber so that the inner circumferential surface is pressed against the outer circumferential surface of the shaft member to thereby bring the shaft member and the cylindrical member into frictional connection for transmission of torque. In this torque limiter, a cutting member of the shaft member is locked at the other end portion of a shear valve which communicates with the hydraulic expansion chamber at one end portion thereof.
When the shaft member changes its circumferential position relative to the cylindrical member as a result of the inner circumferential surface of the cylindrical member slipping on the outer circumferential surface of the shaft member due to a load of a predetermined value or larger being exerted on the shaft member or the cylindrical member, the other end portion of the shear valve which constitutes the other end portion of the oil drain is designed to be cut by the cutting member so that the hydraulic oil within the hydraulic expansion chamber is discharged to an exterior portion. By the hydraulic oil being so discharged, the inner circumferential surface of the cylindrical member is no more pressed against the outer circumferential surface of the shaft member, whereby the frictional connection of the shaft member with the cylindrical member is cancelled to cut off the transmission of torque.
The torque limiter has a plurality of scattering prevention covers. Each scattering prevention cover is a cap-shaped member. There are provided the same number of scattering prevention covers as the number of shear valves, and the scattering prevention covers are disposed so as to cover the corresponding shear valves. The cap-shaped members are fixedly screwed to the cylindrical member.
The scattering prevention cover prevents the scattering of oil at the other end portion of the shear valve and within the hydraulic expansion chamber when the other end portion of the sear valve is cut.
With the conventional torque limiter, when the torque limiter is repaired after the shaft member changes its circumferential position relative to the cylindrical member whereby the other end portions of the shear valves are cut, it is inevitable to perform work of removing all the plurality of scattering prevention covers and work of fixedly attaching the plurality of scattering prevention covers again after new shear valves are fitted in the predetermined positions. Consequently, many manhours and much manpower have to be involved to get the torque limiter ready for operation again after the oil within the hydraulic expansion chamber of the torque limiter has been released to the exterior portion, causing a problem that it is difficult to get the torque limiter ready for operation again quickly and smoothly.